A semiconductor chip may be created, for example, by a reduction projection of a mask on which a circuit pattern has been drawn onto a wafer having a resist applied thereon and by repeatedly performing processing such as an etching and a thin film formation. The progressive reduction of the scale of semiconductor processing demands the use of radiation of a further short wavelength.
Thus, a research is being made on a semiconductor exposure technique which uses a radiation of an extremely short wavelength of 13.5 nm or so and a reduction optics system. This type of technique is termed an EUVL (Extreme Ultra Violet Lithography: an exposure using an extreme ultra violet light). Hereafter, an extreme ultraviolet light will be abbreviated as “EUV light”.
Three types of EUV light sources are known for example: an LPP (Laser Produced Plasma: plasma produced by a laser) type light source, a DPP (Discharge Produced Plasma) type light source, and an SR (Synchrotron Radiation) type light source.
The LPP type light source is a light source which generates a plasma by irradiating a target material with a laser beam, and employs an EUV light that is emitted from this plasma. The DPP type light source is a light source which employs a plasma that is generated by an electrical discharge. The SR (synchrotron radiation) is a light source which uses an orbital radiation.
Of those three types of light sources, the LPP type light source is more likely to obtain an EUV light of a higher output power as compared to the other two types because the LPP type light source can provide an increased plasma density and can ensure a larger solid angle over which the light is collected (see Patent Citation 1).
For the EUV light source device of the LPP type, a metal such as tin (Sn) is used as a target material in large part. The EUV light source device of the LPP type is provided with a target supply device. The target supply device heats and melts tin, and makes tin blow out as a droplet from a nozzle having a minor diameter.
It is known that an oxide film is formed on the surface of a stainless steel in a field of a solder bath in which a so-called lead-free solder is used although it is irrelevant to the technical field of an extreme ultraviolet light source device (see Patent Citation 2 and Patent Citation 3).
Moreover, a technique in which a target material is collected for a recycle is also known (see Patent Citation 4).